1. Field of the Invention
The present invention relates to a dual tunnel junction sensor with a single antiferromagnetic layer and, more particularly, to dual sensor components that share a single antiferromagnetic layer.
2. Description of the Related Art
A read head employing a read sensor may be combined with an inductive write head to form a combined magnetic head. In a magnetic disk drive, an air bearing surface (ABS) of the combined magnetic head is supported adjacent a rotating disk to write information on or read information from the disk. Information is written to the rotating disk by magnetic fields which fringe across a gap between the first and second pole pieces of the write head. In a read mode, the resistance of the read sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a current is conducted through the read sensor, resistance changes cause potential changes that are detected and processed as playback signals in processing circuitry.
One type of read sensor is a tunnel junction sensor. The details of tunnel junction have been described in a commonly assigned U.S. Pat. No. 5,650,958 to Gallagher et al., which is incorporated by reference herein. A typical tunnel junction sensor has two ferromagnetic layers (i.e., the pinned and free layers) separated by a thin barrier layer which relies upon the phenomenon of spin-polarized electron tunneling. The free and pinned layers, which may be NiFe or CoFe, are separated by a non-magnetic electrically insulating barrier layer that is thin enough that quantum mechanical tunneling occurs between the free and pinned layers. The pinned layer has a magnetic moment that is pinned in its orientation by exchange coupling with a pinning layer that is made of an antiferromagnetic material. The tunneling phenomenon is electron spin dependent, making the magnetic response of the tunnel junction sensor a function of the relative orientations and spin polarization of the conduction electrons between the free and pinned layers. Ideally, the magnetic moment orientation of the pinned layer should be pinned 90.degree. to the magnetic moment orientation of the free layer, with the magnetic direction of the free layer being able to respond to external magnetic fields. It is possible to improve the sensitivity of a tunnel junction head structure by using multiple tunnel junction sensors. One problem with this scheme is that it requires multiple antiferromagnetic layers. Since the antiferromagnetic layers are relatively thick, using multiple antiferromagnetic layers increases the size of the read gap of the tunnel junction read head which equates to a reduced linear read bit density along a track of the rotating disk. Therefore, it may not be possible to insert more than one antiferromagnetic layer within the read gap for future ultra high areal density heads. There is a strong-felt need of increasing the sensitivity of the tunnel junction head structure with multiple tunnel junction sensors without significantly increasing the size of the read gap.